This invention relates in general to brake systems and in particular to braking systems for vehicle wheels. The term "vehicle," as used herein, is intended to refer to bicycles, motorcycles and the like. The brake system of the invention is a replacement for conventional vehicle braking systems.
A bicycle braking system generally comprises a caliper having a pair of friction brake pads that straddle the bicycle tire for engagement with the sides of the wheel or rim. The brake is activated by a cable that closes the caliper to frictionally engage the pads with the rim. A motorcycle brake system includes one or two brake disks affixed to the wheel and which are engaged by automotive type disk brake caliper assemblies. Both brake systems are relatively complex and expensive and, particularly in the case of bicycles, difficult to maintain in proper adjustment, which is required for safe operation. The adjustment problem is severe because of the difficulty in keeping the rather delicate spoked wheels "in line," i.e. where the side of the rim lies in one plane. A "wobbly" or "out of line" wheel is very common. Such a wheel does not run "true" but moves from side to side as it rotates. Since the brake pads are adjusted outwardly to normally avoid contact with the rim, they are quite far apart for misaligned or wobbly wheels. This directly affects the actuation distance of the brake pads, making it difficult, or impossible, to obtain sufficient braking force.
Another problem with both bicycle and motorcycle brakes is their unreliable operation under adverse conditions, i.e. in the presence of contaminating materials such as water and dirt. These systems are also very inefficient from a space utilization point of view, and are not aesthetically pleasing.
The brake system of the invention incorporates a brake cable or band that applies circumferential friction loading directly to the wheel where the large surface area of the rim serves as a heat sink. The effectiveness of the heat sink is enhanced by the wheel's rotation through the air. The wheel is manufactured with one or two circumferential brake troughs or lips extending outwardly from the rim sides. Preferably a casting or an extrusion process is used. It is conventional for bicycle wheels to be extruded, formed into a loop, and subsequently cut to length and welded. With the invention the lip that forms the trough for the braking cable may be integrally formed at very little added cost. The lip is outwardly displaced from the side of the wheel sufficiently to enable the cable to clear the sides of the tire. A single lip is adequate for most applications. For heavy duty brake applications, a lip is provided on each side of the wheel. In accordance with the preferred embodiment of the invention, a bicycle brake is fabricated with a close wound steel cable that is encased over its operative braking portion in a Kevlar (.TM. ) aramid fiber jacket for its excellent friction and wear properties. For heavy duty applications, a dual cable within a single jacket or a flat band for increasing the amount of surface friction area may be used.
One end of the braking cable is secured to the frame and wrapped around the trough in the direction of wheel rotation. The other end is tensioned by operation of a hand lever. The frictional force on the cable combines with the input force from the hand lever to effectively provide a self-energized power assisted braking action. The inventive system significantly reduces the brake lever force requirement of comparable conventional systems and provides the operator with a safer, easier to operate braking system that provides a sensitive "feel" for better brake modulation.